Star
Tracker

Lightweight, Low Power Inexpensive Star Tracker

 PI: Dr. Raymond Sedwick, Grad RA: Kara Huffman

*AeroAstro FAR-MST Phase I proposal

Unfortunately, current star trackers strive to maximize attitude sensing performance above all else.  They incorporate extremely complex systems to process numerous stellar patterns as quickly as possible, and they contain expansive on-board star catalogs that include tens of thousands of stars for the most exact star matching techniques.  Although these characteristics allow for highly competent systems, these star trackers are inaccessible to smaller satellites due to their large mass quantities, high power consumption rates, excessive memory requirements, and immense cost measures.

MIT’s Space System’s Laboratory (SSL) and AeroAstro, Inc. are currently developing two star trackers, LIST (Lightweight Inexpensive Star Tracker) and FAR-MST (Fast Angular Rate Miniature Star Tracker), that will aspire the design and manufacture of a more commercially viable star tracker for micro-satellites and small-scale spacecraft.  LIST is being developed for the Missile Defense Agency (MDA) under an AeroAstro subcontract to MIT, whereas FAR-MST is being developed for the Air Force Research Lab (AFRL) through consulting efforts of the PI with AeroAstro directly.  The figure below describes the attitude sensing techniques that will be implemented with LIST and FAR-MST.  The general focus of LIST is to achieve relative attitude information for moderate tumble rates.  This will be accomplished by comparing the movement of stellar patterns between consecutive images.  FAR-MST will achieve absolute attitude information at higher tumble rates and be able to solve Lost in Space (LIS) problems through image comparison to onboard star catalogs and star streak patterns.  LIST, will be able to determine relative attitudes at tumble rates up to 1°/s, and FAR-MST will determine tumble rates up to 10°/s [2, 3].  While taking advantage of robustness of current star trackers, LIST and FAR-MST hope to initiate a new genre of star trackers that better balance performance accuracy with size, weight, complexity, power consumption, and expenditure metrics.

*Anderson, FAR-MST Phase 1 SBIR Final Report

While AeroAstro is designing, constructing, and testing the star tracker hardware, SSL is responsible for developing and testing the algorithms that will decipher and process the stellar signal.  The main algorithms include functions that distinguish noise from actual star signal, precisely centroid stars, and match particular star patterns between consecutive images so that attitude rates can be acquired over time.  Currently, the centroiding and pattern matching codes are being improved and translated into a compilable language that can be tested on the actual LIST and FAR-MST star trackers.  Throughout the algorithm creation process, SSL has tested the functions on both computer simulated images and nighttime sky photographs to verify that mission requirements are being successfully achieved.  Improvements are continually being made to minimize memory storage and computation time and maximize algorithm efficiency and robustness.  The majority of the remaining work includes further optimizing the centroiding and pattern matching algorithms to solve the Lost-in-Space problem in FAR-MST and confirming that each code can be successfully run on the LIST and FAR-MST star trackers.

References

 [1]       AeroAstro, Inc. FAR-MST Phase II Proposal; proprietary.

[2]        AeroAstro, Inc. LIST Phase II Proposal, proprietary.

[3]        AeroAstro, Inc. FAR-MST Phase I Proposal, proprietary.